Gun aiming post having parabolic reflecting surface



March 16, 1948. L. H. BROWN 2,437,677

GUN AIMING POST HAVING PARABOLIC REFLECTING SURFACE Filed June 25, 1944 Fj: QEI- 56 57 29 2a 30 29 28 Jame/WM LED H ERDWN,

Patented Mar. 16, 1948 nitiiiibii UNITED STATES PATENT OFFICE GUN AIMIN G POST HAVING PARABOLIC REFLECTING SURFACE 8 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

The present invention relates to an optical device and aiming post for use in the indirect firing of cannon.

Among the objects of the invention is the provision of an aiming post which furnishes a broad beam of parallel light rays, which, when viewed from any point in the beam, in a. direction parallel to the parallel light rays thereof, gives rise to an image of a fiducial line, slit or reticle, the image obtained at all points being produced from light rays coming from the same fiducial line, slit or reticle.

A further object of the invention is the provision of an optical device suitable for establishing a line of reference from which angles may be measured regardless of the purpose of measuring said angles.

At present, in the indirect firing or laying of a howitzer, mortar or other cannon use is made of an aiming post as a point from which to measure the azimuth of the howitzer, mortar or other cannon, This aiming post consists of a tubular rod about one inch in diameter and several feet long. One end of the rod is pointed for embedding in the ground. The howitzer or mortar sight is sighted n the post or a part thereof, and changes which are required in the azimuth of the howitzer or mortar are all referred to the aiming post, i. e., to the line of sight between the sighting means, e. g., collimator sight or telescopic sight, and the aiming post when the sighting means is sighted on the aiming post.

If the direction of displacement of the howitzer, mortar or other cannon, due to recoil, is not parallel with the line of sight of the sighting means on the aiming post, which condition of parallelism does not usually exist, a new line of sight arises, and therefore errors are introduced in applying changes in azimuth directed by the observer of the effect of the fire.

The present invention eliminates these errors and besides enables the aiming post to be placed much nearer to the mortar or howitzer or other cannon than the conventional aiming post described above, without introduction of appreciable error in applying fire correction data.

Two embodiments of the invention are illustrated in the accompanying drawings. In these drawings wherein the same reference character indicates the same or corresponding parts,

amended April 30, 1928; 370 0. G. 757) Figure l is a plan View of an aiming post cons'tructed according to the invention.

Figure 2 is a front elevation of the embodiment shown in plan in Figure 1.

Figure Bis a section on the line 3-3 of Figure 2.

Figure 4 is a cross section on the line 44 of Figure 1.

Figure 5 is a perspective View of the socket which is used to hold the slit forming means or reticle, and in which, when necessary, a flash light may be secured for the purpose of illuminating the said slit or reticle,

Figure 6 is an enlarged longitudinal section of the socket shown in section in Figure 1 and in perspective in Figure 5.

Figure 7 is a top plan of another modification of the invention.

Figure 8 is an enlarged cross section on the line 8-8 of Figure 7.

In the said drawings, a portion of a parabolic cylinder is indicated by the numeral I. The concave side of this parabolic cylindrical portion is specular, that is to say it has the properties of a mirror. The said parabolic cylindrical portion is preferably formed from a strip of thin sheet metal which has been plated or polished on the side which is to be the concave specular side of the said portion. The said strip is shaped or flexed lengthwise into the portion of a parabolic cylinder during the assembly of the device, as hereinafter explained. The specular or mirror surface thus formed may be considered as generated by a straight line generatrix moving along in intersecting relation with a portion of a parabola, normal to the plane of such parabola.

Parabolic cylindrical portion I is carried in a housing 2, shaped more or less to conform with said portion. This housing comprises a rear wall 3, a top wall 4, a bottom wall 5, and end walls 6 and 1. Each end wall joins with the rear Wall and with the bottom and top walls. The front of the housing 2 is open as shown in Figures 2 and 3.

Ears 8 are formed on or secured to top wall 4, bottom wall 5, end wall 6 of housing 2 and receive the socket or chamber forming means 9. Socket 9 is secured to said ears by means of screws or rivets.

The parabolic cylindrical portion l is held in position in housing 2 by means of plates I0, I I, I2 and I3 shaped to conform with the inner contour of the casing 2 and with the parabolic curve of the parabolic cylindrical portion l. Plates Ill and II are secured to the top and bottom respectively of housing 2; and plates l2 and I3 are also secured to the top and bottom respectively of the housing 2. These plates may be secured to the top and bottom of housing 2 by means of screws, rivets or in any other suitable way, such securing means being indicated by numeral I4. Sufficient space is provided between plates III and I2 on the top of the housing, and between plates II and I3 on the bottom of the housing to accommodate the parabolic cylindrical portion I which extends from the top wall 4 of the housing to the bottom wall 5 thereof. In other words, the parabolic cylindrical portion I is as high as the inside height of the housing but with sufiicient allowance in dimensions to permit its insertion and assembly in the housing as shown in the drawings and as hereinafter further explained.

The parabolic cylindrical portion I may be assembled in housing 2 as follows: Plates I2 and I3 are secured respectively to the top and bottom of the housing. Then the sheet metal specular strip from which the parabolic cylindrical portion is to be formed is inserted in the housing against the inner edges of plates I2 and I3. Plates III and II are now inserted in the housing in the position shown in the drawings, and pushed towards the plates I2 and I3 so as to bow the strip of sheet metal into the form of a portion of a parabolic cylinder between plates I0 and I2 at the top of the strip and between plates II and I3 at the bottom of the strip. The inner edges of plates III and I I are shaped to the same parabolic curvature as the inner edges of plates I2 and I3. It will, therefore, be seen that the strip of sheet metal assumes lengthwise the form of a portion of a parabolic cylinder. Plates I0 and II are now secured in fixed position in the housing 2.

The socket 9 is provided with a slot 20 in its rear wall 2|, and a shoulder 22 is provided along the edges of this slot to provide a depression within which the ground glass, or ground plastic plate 23 fits. Plate 23 is flush with the surface 24 of rear wall 2I of socket 9. Two slit forming plates 21 are secured upon the surface 24 by means of screws 28 which pass through slots 29 in the slitforming plates and engaged threaded holes in the rear wall 2I of socket 9. The adjacent edges 30 of slit-forming plates 21 are bevelled to a sharp edge so as to form a knife edge slit between them. Screws 28 and slots 29 in the slit-forming plates 21 permit the width of the slit to be adjusted.

Glass or plastic plate 23 is preferably ground only on the side contiguous with slit-forming plates 21, the other side being smooth and transparent. This ground lass or plastic plate constitutes means for diffusing light that passes through the slit to the parabolic cylindrical portion I. The slit, therefore, should lie between the diifusing means and the parabolic cylindrical portion I,

The socket portion 9 together with the ground glass or plastic plate and the slit forming means carried thereby is so located on the housing 2 that the slit, or narrow slot, between the edges of bevelled portions 30 of slit-forming plates 21 lies at the place which is the focus of the parabolic cylinder of which portion I is a part. The slit therefore coincides with this focus.

Two straps 35 are secured to the rear wall 3 of housing 2. These straps slidingly engage the two posts or stakes 36. Each strap is provided with a thumb screw 31 engaging a threaded hole through the strap. When the thumb screws are screwed inwardly of the strap, they engage the posts 36 and clamp the housing 2 in fixed relation to the posts 36. Thus, the position of the housing 2 may be adjusted in relation to the length or height of the posts. The posts are pointed at their lower ends 38 to facilitate embedding the lower ends in the ground.

Since the slit between the two slit members 21 coincides with the focus of the parabolic cylinder of which the portion I forms a part, light passin through the slit to the portion I will be reflected by the latter as parallel rays of light.

The top of housing 2 is provided with sighting means consisting of a V-front sight 40 and a peephole rear sight 4 I. The line of sight of this sighting means is parallel with the parallel light rays I52 which are produced by the portion I of the parabolic cylinder reflecting the rays 63 of light from the slit. In other words, the line of sight of the sighting means is parallel with the axis of the parabolic cylinder of which portion I is a part. Thus an image of the reticle, or aiming mark, may be seen and sighted upon from the gun, for any position of the sight between the boundary rays 62, that is, the rays 62 at the extreme right and left as viewed in Fig, 3; and the gun may be maintained at constant azimuth so long as its sight remains between these boundary rays and is held directed upon the observed reticle image by any necessary azimuthal adjustments of the gun and sight as a unit.

When ordinary day light or solar light does not provide sufiicient illumination of the slit between slit forming members 21, the bulb end of an ordinary cylindrical flash light may be inserted into the open end of the socket 9 and secured therein in any convenient manner.

Reference is now made to the modification of the invention illustrated in Figures 7 and 8. In this modification of the invention, the housin corresponding to the housing 2 of the modification described above consists of a top 44, a bottom 45, channel back 46, and channel ends 41 and 48. The edges of top 44 and bottom 45 respectively adjacent channel back 46 are curved according to the parabolic curve of the parabolic cylinder. In this modification, the specular sheet metal strip which forms the portion 49 of the parabolic cylinder is secured between the channel back 46 and the parabolically curved edges of top 44 and bottom 45 of the housing. Back 46 is curved to conform to the curvature of the adjoining edges of top 44 and bottom 45, and is secured to these by means of screws 50, or other fastening means, as shown in the drawings. Ends 41 and 48 are secured to top 44 and bottom 45 in a similar manner.

In the modification of the invention illustrated in Figs. '1 and 8, a single strap 5|, secured to back 46, is employed to form a sliding connection with post 52, which latter corresponds with posts 36 of the other modification described above. Thumb screws 53 which pass through the strap 5I, may be used to clamp the housing in fixed position on post 52.

Socket 55, corresponding to socket 9, is secured to the housing or device by means of ears 56. These ears 5B correspond with ears 8 of the previously described modification of the invention.

Socket 55 carries a ground glass or plastic light diffusing member and slit forming members, these being constructed and arranged in the same manner as shown in Figures 3, 5 and 6 of the other modification of the invention. The bulb end of a flash light 51 is shown inserted within the socket 55 and is held therein by means of a thumb screw 58 threaded through thewall of the socket. The flash light is used at night or on dark days when solar illumination is not sufficient to illuminate the slit. Front and rear sights 59 and 60 are mounted on the top 44 in the same manner as front and rear sights 40 and 4| are mounted on top 4 of the modification of the invention illustrated in Figures 1 and 2.

A line drawn on ground glass or plastic plate 23, in the focus of the parabolic cylinder, may be used as a reticle instead of the slit formed between the two members 21.

In use in in-direct fire, or in indirect laying of a cannon, the device is set up horizontally to the ground at a suitable distance, e. g., to 25 feet from the sighting means, e. g., collimator sight or telescopic sight of the cannon, e. g., mortar or howitzer, in such a manner that the line of sight of the sighting means lies in the beam consisting of parallel light rays 62 and is parallel to the said light rays. This condition exists when the image of the slit between slit forming members 2'! is seen in the telescopic sight along the optical axis thereof, or along the optical axis of the collimator sight. Changes in azimuth of the cannon, or of the cannon sighting means, may now be referred to this condition of parallelism as a reference point for measuring the angles involved in the changes,

The length of the parabolic cylindrical portion l or 49 measured along its curved surface is advantageously chosen so as to give a beam of light rays 62 from about one foot to tWo feet wide measured perpendicularly across the rays 62 and in the claims, the term substantial length is to be interpreted in accordance with this range of dimensions. At any event, the width of the beam, and as a consequence the length of the parabolic cylindrical portion, should be suflicient, that sidewise displacement of the cannon as a result of firing does not cause the line of sight Of the sighting means of the cannon to be displaced sideways out of the beam. Here, of course, it will be understood that the sighting means referred to experiences the same sidewise displacement as the cannon.

The width of the specular sheet metal strip from which the parabolic cylindrical portion l or 49 is formed may, for example, be from one to two inches, although I do not limit myself to these specific dimensions.

In the claims, the top, bottom, side walls, and elements of the parabolic cylindrical surfaces have been defined in the position in which those portions are normally located in the particular use of the device illustrated. It will be understood that this is for clarity and simplicity of expression and that it is not intended thereby to restrict use of the device to the particular position shown.

' I claim:

1. In an aiming post for laying guns in azimuth, a housing having one side open, a portion of a concave parabolic cylindrical reflector surface mounted in said housing opposite said open side and fully observable through said side from a remote position, illuminable means carried by said housing at the focus of said surface and forming a narrow elongated reticle parallel to the generatrix of said surface, the image of said reticle being observable as a narrow line for all positions of the eye laterally between the boundary reflected rays.

2. An aiming post for laying artillery, comprising, a housing having a first side wall shaped as a portion of a parabolic cylinder with normally vertical generatrix, the side of said housing opposite said first wall being open, a para bolic cylindrical concave reflector positioned in said housing adjacent said first wall and unobstructedly viewable through said open side, the generatrix of said reflector surface being normally vertical, illuminable means mounted in said housing forming a narrow elongated vertical reticle line at the focus of said reflector, said line being parallel with the generatrix of the surface of said reflector, the image of said reticle being observable in said reflector as a narrow vertical line for all positions of the eye laterally between the boundary reflected rays, and a mounting bracket fixed to said housing for adjustably securing said housing to a fixed post.

3. In an aiming device for laying artillery, a housing having a generally flat top and bottom and having one side wall shaped as a portion of a parabolic cylinder with normally vertical generatrix, the side of said housing opposite said wall being open, a concave mirror formed as one side of a parabolic cylinder and mounted in said housing adjacent to and extending along said wall and viewable through said open side, said mirror having a normally vertical generatrix, means forming a chamber in said housin and having a narrow vertical slit in one wall at the focus of said mirror, whereby when said chamber is illuminated to thereby illuminate said slit, said slit forms on said mirror an illuminated reticle parallel with said generatrix, the image of said reticle being observable as a narrow vertical line for all positions of the eye laterally between the boundary reflected rays, and means mounting said housing for vertical adjustment on and with respect to a supporting surface.

4. An aiming post comprising a housing having a generally plane parallel top and bottom and a side wall, the side of said housing opposite said wall being open, a concave mirror mounted in said housing adjacent said side wall and unobstructedly viewable through said opening, said mirror being formed as one leg of a parabolic cylinder with normally vertical generatrix, means carried by said housing forming a chamber adjacent the focus of said mirror, there being a narrow vertical slit in one wall of said chamber at said focus, whereby when said chamber is illuminated to thereby illuminate said slit, an image of said slit is observable as a narrow vertical line for all positions of the eye laterally between the boundary reflected rays, and sighting means carried by said housing and defining a line of sight parallel to the rays from said slit reflected from said mirror.

5. An aiming post as in claim 4, said chamber having an opening in its said wall, a pair of plates having vertical, spaced knife edges secured over said opening to define said slit, said plates being relatively horizontally adjustable to vary the width of said slit, and light-diffusing means extending over and across said slit on the side of said plates remote from said mirror, said chamber being formed to receive a source of artificial illumination.

6. An aiming post as in claim 4, a mounting stake adapted to fixedly engage a supporting surface, a bracket carried by said housing to slidably and rotatably engage said stake, and means carried by said bracket to engage said post and releasably fix said housing in adjusted position relatively to said stake.

'7. In an aiming post for artillery, a support, a concave mirror mounted on said support and having its reflecting surface in the form of a leg of substantial length, of a parabolic cylinder having a normally vertical generatrix, means carried by said support to form an illuminated narrow reticle at the focus of said parabolic reflecting surface, said reticle being parallel with the generatrix of said surface, the image of said reticle being observable as a narrow vertical line for all positions of an observer laterally between the boundary reflected rays, and a bracket carried by said housing for adjustably securing said housing to a fixed post.

8. In an aiming post as recited in claim '7, and means carried by said support determining a line of sight parallel with said reflected rays.

LEO H. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Grubb Sept. 24, 1901 Beidler Mar. 1, 1904 Schanz Apr. 9, 1907 Stutzer July 21, 1925 Willson Mar. 12, 1929 Rice June 11, 1935 Morelle Mar. 9, 1943 Luckiesh et al Mar. '7, 1944 Chwalow Sept. 19, 1944 FOREIGN PATENTS Country Date Great Britain May 12, 1914 Great Britain Oct. 28, 1935 

